Cell theory originated from microscopic observations of cork and dental plaque

Before discovering cells, life was believed to emerge suddenly from inorganic matter

Popularized by Aristotle in the 4th century BCE, spontaneous generation was used to explain phenomena like mice appearing in seemingly sealed grain storage. The invention of the compound microscope in the late 16th century led to the identification of cells as the basic unit of life, but it was not until 1855 that their origin from preexisting cells was established.

Learn how chloroplasts—the photosynthesis factories—may have once been independent cells

Possessing DNA of their own that differs from that of their host cell and surrounded by cellular membranes like those observed in bacteria, chloroplasts are believed to have evolved from a cyanobacterial cell. The endosymbiotic theory explains that these organelles were absorbed into larger cells, leading to the photosynthetic cells seen today.

Evidence suggests the first cells on Earth were bacteria

About 4 billion years ago, these single-celled organisms harvested carbon dioxide and sunlight to produce their own food and oxygen, setting the stage for the evolution of oxygen-breathing life forms. Archaeabacteria, which thrive on inorganic molecules in extreme habitats on Earth today, were also among the earliest organisms.

Cells are categorized by the presence of contained genetic material and other organelles

While prokaryotes contain one or more cells with free-floating genetic material in a region called the nucleoid, eukaryotes possess a nucleus specialized for DNA storage. Plant cells possess cell walls—a reinforced structure surrounding their membrane—made of cellulose, while fungal cell walls contain chitin. Animal cells have lysosomes housing enzymes that break down biomolecules. (Some readers may experience a paywall.)

The secret lives of cells

Cutting-edge microscopy has revealed previously unseen interactions of biological molecules within their cellular environment, enabling scientists to observe and analyze the molecules in a holistic view. This podcast explains the minute advancements made over the last few decades in observing cells, revealing how scientists have come and what the future holds for the field.

Some organisms are composed of a single cell visible to the naked eye

By incorporating tough, cellulose-rich cell walls, rapid movement of molecules via cytoplasmic streaming, and other biological techniques, some unicellular organisms can bypass the physical limitations that restrict the size of cells. Organisms such as the Stentor coeruleus and Acetabularia can be seen without microscopes.

An overview on germ theory, the crucial framework developed by Louis Pasteur

Germ theory of disease is based on the concept that many diseases are caused by infections with microorganisms, typically only visualized under high magnification. Read this general overview to understand the basic framework which allowed for development of vaccines.

The earliest known cardiovascular system dates to 520 million years ago

The earliest evidence of a cardiovascular system and blood-like substance may date back to the Cambrian period in an ancient arthropod. This 2014 academic article includes images of the ancient cardiovascular system, which remains one of the most detailed samples of Cambrian arthropod anatomy.

The term 'cancer' is 3,000 years old

Around 400 BCE, Hippocrates is said to have named masses of cancerous cells "karkinos"—the Greek word for crab. Science and medical historian Dr. Howard Markel discusses a few hypotheses on why Hippocrates named the disease after a crab and how well cancer was understood in the ancient world.

The quantum model of the atom resulted from over two millennia of scientific thinking

In 440 BCE, Democritus proposed that everything was made up of tiny particles surrounded by empty space, which varied in size and shape based on the substance's properties. It was not until the 20th century that experimental evidence validated elements of Democritus' model.

The cholera bacteria was first isolated in 1854—but the discovery was largely ignored

The pathogen was isolated by the Italian physician Filippo Pacini in Florence, Italy, though his discovery was largely ignored in favor of the popular miasma—bad air—theory of disease at the time. The pathogen was separately isolated about three decades later by German microbiologist Robert Koch.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Cellular aging and deterioration leads to tissue (and overall) aging

Cells are the building blocks of life, forming tissues and organs that keep our bodies working. As we age, cellular changes have progressive consequences on both the structure and function of our organs. This article examines this complex relationship as it relates to the incremental changes associated with aging.

Chronobiologists study the effect of time on biological cycles

Circadian rhythms were first observed in the 1700s, when French astronomer Jean-Jacques D'Ortous de Mairan put a plant in a dark room and watched it still respond to day and night cycles, setting off further studies about specific light-dark biological cycles, an area of inquiry that continues today with the human "clock proteins" at the molecular level.

What a tiny marine worm can tell us about our brains

Meet the amphioxus, a small eel-like animal that has a lot to teach us about brain evolution. The genetic roots of our brains can be seen in these unusual creatures. This three-minute educational video focuses on the evolutionary history of the human brain through these odd little critters with a 500-million-year-old history.

The origin of the symbiotic relationship between corals and the algae that feed them

An analysis of fossilized reefs from northern Africa and Germany suggests that shallow water corals and photosynthetic algae formed a mutualistic partnership between 419 and 359 million years ago. The discovery was made by analyzing nitrogen-isotope ratios in the fossils, which differ depending on whether algae are present, due to various chemical processes.

Exploring the link between history, art, and anatomy

Throughout centuries, art has played a vital role in sharing—and furthering—scientific understanding. This largely began in 1543 when physician Andreas Vesalius worked with an artist and engraver to transform learnings from his dissections into...

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

The first identification of Alzheimer's was made in 1906

The first case of Alzheimer's disease dates to the early 20th century when Dr. Alois Alzheimer had 51-year-old Auguste Deter as a patient. Deter struggled with sudden memory issues and aggressive, irrational behavior. After Deter's death, Alzheimer examined her brain and found strange collections of molecular pileups.

A weed from the mustard family facilitated the molecular era of botany

The small genome and rapid growth cycle of Arabidopsis thaliana have made it an ideal organism for genetic studies, with over 100,000 research papers exploring topics such as disease resistance, stress tolerance, and response to light. The first studies were done on plants that grew from seeds saved during the Hungarian Uprising of 1956.

The theory of plate tectonics was not initially accepted until evidence became undeniable

Alfred Wegener proposed continental drift—the movement of large landmasses—in 1912 to explain why similar rock layers, plant and animal fossils, and glacial deposits were found on continents that were then unconnected. In the early 1960s, this was combined with evidence of seafloor spreading, mantle convection in Earth's interior, and earthquake and volcanic data outlining plate boundaries to produce the accepted theory.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

How do stem cells actually work?

Stem cells are unspecialized cells that can develop into various cell types while also making exact replicas of themselves. This amazing ability has made stem cells a candidate to treat a wide variety of diseases and conditions—though the vast majority of potential therapies remain in the research stage.

Watson and Crick revealed DNA's double-helix structure using others' key findings

Their 1953 model, made from cardboard cutouts, explained how DNA stores genetic information through base pairing. Rather than experimenting and collecting their own data, they incorporated patterns and data from other scientists through trial and error.

Wilhelm Wundt's place in the history of psychology

While ancient philosophers considered the central problems of psychology, it was Wilhelm Wundt who first called himself one. Here's a quick video overview of his contribution.

The name ‘tardigrades’ comes from the Latin word for ‘slow walkers’

Before being renamed for their movements, German pastor Johann August Ephraim Goeze called them Kleiner Wasserbär—little water bears—in the first published observations of the creatures in 1773. He noted their voracious appetite made them seem like bears under a microscope.

Wood that changed the color of water was the earliest recorded example of fluorescence

Lignum nephriticum, a tea used to treat kidney and urinary illnesses, was described in the 16th century as derived from white wood that turned water a bluish hue. However, in the 17th century, accounts described the wood as reddish and creating a kaleidoscope of colors in water. In 1915, the sources were identified as two different woods, which absorb UV radiation and emit visible light.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Coral reefs get their colors from zooxanthellae—microorganisms that line corals' digestive tracts and provide them with sugars in exchange for a home within this protective tissue.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

The concept of phantom limbs, the perception that amputated limbs are still present, dates back to a French military surgeon in the 16th century.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Ebola is a filovirus, meaning it resembles a thread under a microscope, though it sometimes twists and can resemble a bowl of spaghetti.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

Poison ivy was sent to Europe in the 1600s as an exotic, ornamental oddity, where it was purposefully grown in the English royal gardens at Kew, the Faculty of Medicine in Paris, and a few other locations.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

Learn more about the history of fireworks, which dates back to an accidental invention during an alchemist's quest for information about immortality.

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

SpongeBob exemplifies Aristotle's philosophy for living well because he understands that happiness doesn't come from external factors like money, recognition, or power.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

The name 'Silicon Valley' arose from the founding of Shockley Semiconductor Laboratory in Fairchild Semiconductor in 1956-57, founded near Stanford University in Palo Alto

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

Trace how the Bill of Rights, inspired by centuries of political theory, took shape between 1774 and 1789.

Georgia O'Keeffe's flower paintings are often assumed to be sexual, though the artist claimed she was simply interested in highlighting the beauty of flowers that most people neglect

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'